PREPARATION OF GOLD-CHIP WITH OH-AFFINITY FOR SURFACE PLASMON - - PDF document

18TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS

1 Introduction Surface plasmon resonance (SPR) sensor is generally used to analyze the change of bio/nano- materials onto gold film. The advantages of SPR sensor as compared with other sensing techniques are their ability to provide real-time and label-free detections for the direct and continuous monitoring

• f analytes [1]. SPR sensor can detect the interaction

between bio/nano-materials in real-time, and then used as powerful sensing system with molecular level, which can be used in research on detection of binding and dissociation events of bio-molecules with label-free [2]. SPR sensor can obtain their sensing signal with small change of reflectance and angle-shift. The sensorgram is affected by interaction between materials at gold film surface [3]. In general, a SPR analysis experiment is performed with gold coated prism with 50 nm of thickness [4]. However, there are some drawbacks; surface of gold film should be immobilized to functional group such as thiol group (SH), as shown in Fig. 1. In established studies using SPR sensor, materials with hydroxyl functional group (OH) are used as target material at sensing experiment. That materials are need to treat self-assembled monolayers (SAMs)

• f OH-terminated thiol on the gold film [5,6].

However, if glass region is revealed by etching gold film, we can detect a material with OH group without SAMs-treatment. Fig.1. Change of surface functionality with OH- affinity for SPR gold-chip. When we prepare OH-revealed SPR chip, gold film should be etched under having certain pattern. SPR chip which region of gold and glass at surface is certain and formal is useful to apply at sensing experiment. Therefore, in this study, we treated gold film with OH-affinity through PDMS patterning and gold

• etching. We used replica molding technology to

fabricate square patterns as a parent mold. After patterning of metal precursor onto gold chip, marked gold and metal precursor was selectively etched. Finally, we obtained OH-revealed gold film with chessboard-type. Gold film which has original (SH- affinity) and novel (OH-affinity) properties could be used to detect the new materials with OH-affinity. 2 Experiment 2.1 Preparation of PDMS pattern We used PDMS (Sewang Hitech Silicone) of Sylgard-184A and DC-184B. Master pattern was prepared with silicon wafer by photo-lithography. First, Sylgard-184A and DC-184B mixed with appropriate ratio, and waited for an hour at room temperature to remove air bubble in PDMS pattern. Throw on master pattern on heating oven at 80oC for 5~6 hrs. After all step, PDMS is solidified and duplicated master pattern [7]. 2.2 Fabrication of SPR chip with OH-affinity

• Fig. 2 represented the preparation of SPR gold

chip with OH-affinity. LUDOX HS-40 (Sigma- Aldrich) was dropped on the gold film of SPR chip. PDMS pattern was put on the gold film and inflict

• pressure. Micro-pattern of LUDOX induced by

PDMS pattern was dried for ready to etching

• solution. First, uncoated gold film is etching and

emerge glass under gold film. The solution mixed 0.6 M KI and 0.09 M I2 was etched localized gold film [8]. Then, LUDOX was selectively removed by

PREPARATION OF GOLD-CHIP WITH OH-AFFINITY FOR SURFACE PLASMON RESONANCE SENSOR BY MICRO- CONTACT PRINTING

So Hyang Shin, Beum Jin Park and Younghun Kim* Department of Chemical Engineering, Kwangwoon University, Seoul 139-701, Korea

* Corresponding author (korea1@kw.ac.kr)

Keywords: surface plasmon resonance, OH-affinity, patterning, PDMS

0.1 M NaOH etching solution [9]. After all step, SPR chip ready to OH-affinity. Fig.2. Scheme of preparation of SPR gold-chip with OH-affinity. 2.3 Preparation of OH-affinity and analysis with SPR sensor The etched SPR chip was treated with 3- aminopropyltriethoxysilane (APTES) for 3 hours. After immobilization of APTES, SPR chip can be sensing Ag ions. Silver nanopowder with < 100 nm (Sigma-Aldrich) was dispersed in pure water, followed by ultrasonic treatment. Then, solution was filtered through a syringe filter (200 nm isopore; Minisart). The change of reflectance index on surface of SPR chip by Ag nanoparticles (AgNPs) is

• btained using SPR sensor (K-mac).

Fig.3. AFM image of Silicon wafer (A), SEM image

• f PDMS pattern (B).

3 Results and Discussion As shown in Fig. 3, silicon wafer made by photo- lithography and that transferred PDMS pattern. We have prepared PDMS is based on replica molding [10]. The advantage of replica molding is that we can obtain completely identical pattern with original

• pattern. Transferred PDMS pattern was made

reverse phase of silicon wafer. Before curing, liquid

• f PDMS was poured empty space of silicon wafer.

In this study, only island pattern is used. The island pattern has the surface of same form at all direction, whereas the line pattern has the different surface depending on direction. In case of line pattern, the reflectance index of SPR light source will be influenced on the direction. Fig.4.SPR angle etched SPR chip for OH-affinity

• Fig. 4 showed step for preparation of SPR gold
• chip. The SPR angle increased as a function of both

the thickness and the dielectric constant of the

• rganic layers on the gold film, because a smaller

change in refractive index or layer thickness at the sensor surface would cause a clear wavelength shift

• f the resonant wavelength in SPR-reflected spectra.

Patterning of LUDOX on SPR chip induced a lot of angle-shift about 25.5° because cured LUDOX pattern was interfered SPR phenomenon. After gold etching step, we obtained SPR chip with chessboard type since patterned site of gold film was existed and un-patterned site was removed. SPR surface be remained two states, maintaining LUDOX and glass

• n the gold chip. At this point, angle data is little
• changed. The patterned LUDOX dominated SPR

chip, and that SPR angle data was shown similar not etched LUDOX patterning SPR angle. Then, we removed LUDOX by NaOH etching. The surface of SPR chip was back to the first state owing to reveal gold film by removing LUDOX. However, angle

peak is not same with peak of bare SPR chip since already un-patterned gold surface was been etched. For this reason SPR chip are ready for OH-affinity. Fig.5. SPR angle bare SPR chip (A), etched SPR chip (B) treated APTES and sensing AgNPs. The SPR angles of the bare and etched SPR chip were measured the amount of angle shift (Fig. 5). Angle-resolved SPR data was plotted for the bare SPR chip and AgNPs adsorbed treated APTES of SPR chip surface (Fig. 5A). Bare SPR chip little shifted angle data about 0.4°, compared to APTES/gold chip. It might be due to functionalization of assembled amine group (-NH2

+)

• f APTES on gold film surface of SPR chip [11].

Finally, treated SPR chip not activated AgNPs. Not matched activation site of AgNPs and SPR chip, so angle data were not changed. Etched SPR chip showed difference SPR graph (Fig. 5B). The surface had changed previous step. Regions of removed and existed gold film were different surface. Cause ATPES acts differently on each surface. The surface

• f gold film was shown a propensity same with bare

SPR chip, whereas the surface revealed glass because of etching step assembled silane group. Then, amine group of APTES activated as adsorption site of AgNPs. The adsorption of AgNPs in the surface of activated amine was affected on the SPR phenomena, and that induced the change of angle and reflectance. The reflectivity was measured in real time as we changed conditions on the gold surface (Fig. 6A) and that scheme is showed in Fig. 6B. After the SPR detector was moved to 50°, it can analyze adsorption

• f AgNPs in real time. At 337sec, solution of AgNPs

was injected into cell. Then, reflectance increase from 26.44 to 27.67 in 6~7 min, owing to the adsorption of AgNPs on the amine group onto gold surface.

• Fig. 6.Time-resolved SPR data obtained as AgNPs

adsorption in the amine activated site (A), and scheme of AgNPs adsorption in the activated amine surface (B). In conclusion, this study showed that OH-revealed SPR chip can be useful in sensing experiment by detecting AgNPs. That was combined with amine functional group immobilized on glass of SPR chip. Through this result, we confirmed that this chip will be applied to analyze materials with hydroxyl group by using SPR sensor, without binding material with thiol functional group. Furthermore, this chip has dual function that SH-affinity and OH-affinity. References

[1] E. Zubritsky “Product Review: New choices for SPR”. Analytical Chemistry, Vol. 72, No. 7, pp 289 A-292 A, 2000. [2] M. Adamczyk, P. G. Mattingly, K. Shreder, Z. Yu “Surface Plasmon Resonance (SPR) as a Tool for Antibody Conjugate Analysis”. Bioconjugate Chemistry, Vol. 10, No. 6, pp 1032-1037, 1999. [3] X. Caide, S. F. Sui “Characterization of surface Plasmon resonance biosensor”. Sensors and Actuators B, Vol. 66, pp 174-177, 2000. [4] S. Ekgasit, F. Yu, W.Knoll “Displacement of Molecules near a Metal Surface as Seen by an SPR- SPFS Biosensor”. Langmuir, Vol. 21, No. 9, pp 4077-4082, 2005. [5] N. Kanoh, M. Kyo, K. Inamori, A. Ando, A. Asami,

• A. Nakao, H. Osada “SPR Imaging of Photo-Cross-

Linked Small-Molecule Arrays on Gold”. Analytical Chemistry, Vol. 78, No. 7, pp 2226-2230, 2006. [6] L. K. Wolf, D. E. Fullenkamp, R. M. Georgiadis “Quantitative Angle-Resolved SPR Imaging of DNA- DNA and DNA-Drug Kinetics”. Journal of the American Chemical Society, Vol. 127, No. 49, pp 17453-14759, 2005. [7] Y. Xia, G. M. Whitesides “Soft lithography”. Angewandte Chemie International Edition, Vol.37, pp 550-575, 1998. [8] M. Kohler “Etching in Microsystem Technology”. WILEY-VCH, 1999. [9] Q. Zhang, T. Zhang, J. Ge, Y. Yin “Permeable Silica Shell though Surface-Protected Etching”. Nano Letter, Vol. 8, No. 9, pp 2867-2871, 2008. [10] A. Perl, D. N. Reinhourdt, J. Hiskens “Microcontact Printing: Limitations and Achievement”, Advanced Materials, Vol. 21, pp 2257-2268, 2009. [11] X. Sun, W. Wei, “Electrostatic-Assembly-Driven Formation of Micrometer-Scale Supramolecular Sheets of (3-Aminopropyl)triethoxysilane(APTES)- HAuCl4 and Their Subsequent Transformation into Stable APTES Bilayer-Capped Gold Nanoparticles through a Thermal Process”. Langmuir, Vol. 26, pp 6133-6135, 2010.